Information broadcast systems include subscription-based systems in which a user subscribes to a broadcast system that provides programming or other content to the subscriber through a network. Since the programming is broadcasted, it is transmitted once for receipt by all eligible receivers. Access to the content, however, is conditional, depending, for example, on whether or not a subscription fee has been paid for a specific receiver. Such conditional access to the content is realized by encrypting the information (usually the encryption occurs in the transmitter) under control of an authorization key and by transmitting the encrypted content to the receivers. Furthermore, the decryption keys necessary for the decryption of the content are encrypted themselves and transmitted to the receivers. Often, symmetrical encryption techniques are used, where the encryption and decryption keys are the same. Only those receivers that are entitled to the content are able to decrypt the decryption key using a first decryptor. The receivers can then decrypt the content using a second decryptor for decrypting the content under control of the authorization key.
The conditional access described above is provided by Conditional Access Systems (CASs) that encrypt the content, and provide the keys to Conditional Access (CA) modules in the subscribed terminals to decrypt the content. In a mobile television deployment scenario there will be a number of channels, all or some of which will be part of services offered by mobile network operators (MNOs). A service may include content transmitted to terminals, such as mobile TV services. Each type of mobile device may need to communicate with a different CAS to request content and to receive keys for decrypting the content. This dramatically increases the system complexity for the MNOs and the amount of work need to port and update conditional access modules for the mobile devices as needed.